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Abstract

We design an optical setup to extract phase vortices in which the interference intensity of reference light wave and speckle fields produced by random screens with different roughness values in the diffraction region near random screens is obtained. Random screens with different roughness are used as samples. Fourier transform is used to extract speckle phase vortices from the interference intensity, and the experimental results show that the phase vortices can be produced when the roughness of the screen is large enough, and they even may appear on the surface. The density of phase vortices would become larger with an increase of the distances in the diffraction region near the random screen. When the distance is certain, the density of phase vortices becomes larger with the increase of roughness. These results would be helpful for understanding the formation of phase vortices.

(a) The interference intensity pattern of a reference light and a speckle field produced by random screen sample No. 2 at distanceZ=20μm. (b) Local interference intensity pattern of the white squared part in Fig. 3(a). The gray-scale values take arbitrary units and the number of gray-scale level is 32.

(a) The gray-scale image of the spatial frequency spectrum of the image in Fig. 3(a) after Fourier transform. The gray-scale images from (b) to (e), extracted from the image in Fig. 3(a), are the distributions of the phase, the real part, the imaginary part and the intensity, respectively. (f) The same intensity distribution directly recorded by CCD.

Distributions of zero lines of the real and the imaginary parts. The red solid lines and the black dashed lines are respectively the zero lines of the real parts and the imaginary parts. Figures (a1)-(a3), (b1)-(b3), (c1)-(c3) and (d1)-(d3) are for sample No.1, No.2, No.3 and No.4, respectively. Dimensions of each image are8000μm×8000μmand distances are given under each image.